According to a report by investigative group News21, fatigue has been responsible for more than 320 accidents and almost 750 deaths over the last 50 years. A quick nap could reportedly help pilots focus – and it’s safe as long as there’s a system in place to wake them up before they reach deep sleep. Still, the Federal Aviation Administration has never allowed the practice, fearing public concern and litigation if an accident happens mid-nap.

Whether helpful or dangerous, mid-air naps are widespread, even without a copilot. “I can tell you absolutely, but good luck trying to find proof of this, in the military we have single-seat pilots take naps.” says Scott Shappell, a professor at Clemson University who helped write flying policies for military pilots. “If pilots tell you they’ve never napped in the cockpit, they’re lying.”